The electronic storage of data is essential to the management of computer and information systems. Currently, one popular method of electronic storage utilizes magnetoresistive (MR) heads to store and recover data on a disk.
To recover data from a disk, an MR head employs an MR element which changes in resistance according to information stored on an adjacent disk surface. In particular, information is stored on the disk surface as small magnetic domains which produce a series of small localized magnetic fields, and the MR head changes in resistance in accordance with the changing magnetic flux. A current is passed through the MR head, and magnetic information stored on the disk is “read” by measuring the changes in the resistance of the MR head as it passes through the magnetic fields. Specifically, using the value of the current, and by measuring the voltage induced thereby across the MR head, the change in resistance can be calculated. Typically, the voltage across the MR head is measured by converting it to a digital signal using an analog-to-digital (ADC) converter.
FIG. 1 depicts a schematic view of a conventional MR resistance measuring circuit 100. In FIG. 1, ADC 150 is an analog-to-digital converter for converting an analog signal to a digital signal. As can be seen, ADC 150 connects to each side of the magnetoresistive head (hereafter “MR head”) 102, for measuring the voltage vmr across MR head 102. Current source 101 provides a current which is passed through the MR head 102, and which is used in combination with the changes in the voltage across MR head 102 to calculate the resistance Rmr of the MR head.
However, MR heads are sensitive to disturbances introduced into the circuit. One typical disturbance is a common-mode voltage. Fluctuations in common-mode voltage can be caused by numerous sources, including nearby magnetic fields, manufacturing processes, circuit topology, and parasitic circuit elements.
Big fluctuations in common mode voltage, and other jumps in such common mode voltage, may cause damage to the MR head.
While some sources of common-mode disturbances can be detected and addressed, it is difficult to identify and eliminate all causes of common-mode disturbances. Moreover, while some computer chips may be able to tolerate higher amounts of common-mode voltage, other circuits may not be able to function properly once common-mode voltage reaches a threshold level.